A MASSIVE effort by firefighters has ensured a fire which started at St Carthage's Cathedral this morning has not spread further.

>>> GUTTED: First look inside the cathedral after fire

Lismore Fire and Rescue incident controller Brad Harrison said they currently have 40 firefighters at the scene, including a 35m Bronto skylift from Queensland Fire Emergency Serviced Bilinga on the Gold Coast, which will allow them to monitor the situation on the roof of the cathedral.

He said the "damage is severe but not extensive."

Mr Harrison said they were alerted "around 6.30am by an automatic fire alarm."

"Upon arrival the Lismore crew noticed a fire in the rear of the church in a rear anteroom," he said.

"The fire had breached the door and spread into the roof at the rear.

"Firefighters immediately commenced operations and requested five more appliances."

"We now have a Bronto from Queensland on scene and will utilise it for the purposes of observation so the fire will not spread laterally on the roof area."

Mr Harrison said all the firefighters who came from Lismore, Goonellabah, Bangalow, Coraki and Alstonville have done a sensational job.

"The fire has been contained in the area of origin," he said.

"The first crew here were extremely aware that because of the age of the building it could spread quickly, which is why we have committed so many resources.

"Because of dangers with the pitched roof, which has several roof layers, we will remain on scene until the fire is completely out."

Mr Harrison said the steep, high roof did present some challenges.

"It's more about the case of the fact of the age of the building it has two layers of roof on it," he said.

"So the challenge was to get through to all them to make sure the fire was not spreading"

Diocese of Lismore Chancery spokesman Joe Pereiria said he understood that repairs after extensive storm damage to the cathedral roof some years ago has made access by firefighters "more challenging".

Mr Pereiria said the $1.5 million repairs included reinforcing the slate roof tiling.

"The upgrade has made it (the roof) more secure," he said.

"We understand that the combination of water egress this morning and predicted rough weather over the weekend could add to the damage which at this stage we don't really know the extent of."

Mr Pereiria said the Diocese is awaiting advice from emergency services as to when they will be able to reopen the cathedral.